1. Field of the Invention
This invention relates generally to seat positioning mechanisms, and is particularly concerned with seat positioning mechanisms of the type wherein a pair of members slidably connected for telescopic movement with respect to each other are locked in selected positions with respect to each other by friction lock means.
It is well known in the prior art to position seat backs by frictionally engaging a rod with washers having openings receiving the rod. The rod receiving openings of the washers are larger than the rod so that when the washers are positioned transversely of the rod, the rod is free to move. When the washers are tilted from the transverse position, the edge of the rod receiving openings of the washers frictionally engages the rod. Examples of this type of positioning mechanism are disclosed in U.S. Pat. Nos. 980,049; 2,595,240; 2,806,723; 3,206,248; 3,271,071; 3,356,411; 3,419,306 and 3,893,730 as well as German Patent Publication 1852701 of May 30, 1962.
Typically, present mechanisms of this type include an elongated thin-walled housing with a rod slidably received in the housing for telescopic movement with respect to the housing. Lock washers are mounted in the housing, and the rod is received in openings in the lock washers. The lock washers engage a fulcrum located inwardly of the outer boundary of the housing walls. The lock washers are biased to a lock position tilted about the fulcrum by a spring to frictionally restrain the rod against movement. A release mechanism is selectively operable to move the lock washers from the tilted position in frictional engagement with the rod to a transverse, unlock position with respect to the rod, in which transverse position the rod is free to move since the rod receiving openings of the washers are out of frictional engagement with the rod. See, for example, U.S. Pat. Nos. 2,806,723; 3,271,071; 3,356,411 and 3,893,730.
It is obviously desirable to be able to reduce the cross-sectional size of such mechanism so that they can be used in smaller spaces. This is particularly the case with automobile seats where it is necessary to minimize the space required for installation of the positioning mechanism.
A particular problem in designing seat positioning mechanisms of this type is that of providing an adequate frictional force between the lock washers and the rod received in the housing of the mechanism to lock the rod against movement relative to the housing. A major factor in determining the frictional force between the washers and the rod is the distance between the fulcrum engaged by the washers and the longitudinal axis of the rod. This places limits on the cross-sectional dimensions of the housing, as well as the size of the lock washers.
Another factor that effects the size of the mechanism is the manner in which the lock washers are actuated by a release mechanism from their lock positions in frictional engagement with the rod to their unlock positions out of frictional engagement with the rod. Typically, the release mechanism includes a shaft mounted transversely in the housing that extends from one side to the other of the housing. The shaft is generally formed with a cam surface or the like that is movable upon rotation of the shaft into engagement with the lock washers to move the lock washers to their unlock position against the force of a return spring. See, for example, U.S. Pat. Nos. 3,271,071 and 3,893,730. A further expense involved in the manufacture of this type of seat positioning mechanism is the difficulty of securing the release mechanism to the housing of the assembly.